The dynamics of binocular rivalry are influenced by the balance of excitatory and inhibitory neural transmission in the brain. This balance is proposed to play an important role in the neural basis of Autism Spectrum Conditions (ASC). Binocular rivalry has therefore been proposed as a behavioural paradigm to test this theory. Two studies have compared rivalry dynamics between ASC and Control subjects, using stimuli of different levels of visual complexity. While both found results in the expected direction, only one found significant differences in rivalry dynamics between the two groups. First, we hoped to replicate our previous finding of a slower rate of rivalry with longer mixed percepts in ASC in a new, expanded sample of participants. Second, we tested whether this finding was selective for stimuli of a particular level of visual complexity (complex object or simple grating stimuli). 53 participants (26 with ASC, matched for age and IQ) completed twelve 40s trials of binocular rivalry (6 objects, 6 gratings) and 24 control trials. We analysed the rate of perceptual transitions and average percept durations. Repeated measures ANOVAs (with Stimulus Type as a between-subject and Diagnosis as a within-subject factor) revealed a lower rate of switches (F(1, 51) =4.3, p < 0.043) and longer mixed percepts (F(1, 51) =14.7, p < 0.001). These results remained significant when age and IQ were covaried. Group differences in mixed percept durations were confirmed with non-parametric comparisons to be significant in both stimulus conditions, while the difference in switch rate was significant only in the grating condition. We confirm a slower rate of rivalry in ASC, with and increased durations of mixed percepts, and find that this effect is present in simple grating stimuli. This result suggests that an increased excitatory/inhibitory ratio in autism may occur as early as primary visual cortex.